Operation panels and key-related parts of portable telephones, electrical, electronic or acoustic equipments, and the like are made by a keypad (sometimes called as "touch panel" or "rubber switch") made of an elastic silicone rubber.
In this case, when display patterns such as letters or designs are merely formed on a touch base of the keypad, if the keypad is repeatedly touched, the display pattern wears, whereby it is likely for the display pattern to become unclear or disappear. Further, when the display pattern is merely formed on the touch base, not only a high-grade feeling is not given, but also the display pattern is hardly read from the oblique direction.
In order to cope with this problem, a primer is first applied on the display pattern of the silicone rubber-made keypad, and an epoxy resin is then applied thereon and cured, thereby forming a protuberant cured coated film.
However, since the silicone rubber readily causes deformation or elongation and is non-polar, even when the epoxy resin cured coated film is provided via the primer layer, only a few of primers are effective for increasing the adhesion of the epoxy resin to the silicone rubber, so that the touch is repeated in a number of times, the epoxy resin cured coated film is likely to peel apart. Although the improvement in primers is investigated, the present state is that a primer has selectivity such that while it is effective to certain kinds of silicone rubbers, it does not exhibit a satisfactory primer effect against many other kinds of silicone rubbers, i.e., primers which are effective in a wide range of silicone rubbers are not found.
In addition, even when the issue about adhesive properties can be overcome, there are still disadvantages that it is necessary to mix a main agent with a curing agent; it takes a long period of time for the curing; and that since an air is included in at the time of coating, it is necessary to carry out defoaming under reduced pressure. Also, since the epoxy resin cured coated film is hard, if the number of keying increases, it is likely to cause cracks when hit by nails. Further, there is involved a problem that since the epoxy resin cured coated film is not sufficient in weather resistance, it is likely to cause yellowing with a lapse of time (even in case where an ultraviolet light absorber is added, there is still a limit in improvements in the weather resistance).